Method and apparatus for the controlled reduction of organic material

ABSTRACT

There is provided a new and useful method and apparatus for the controlled non-pyrolytic reduction of organic material comprising subjecting the material to microwave radiation in a reducing atmosphere.

CROSS REFERENCES TO RELATED APPLICATIONS

This is a continuation of application Ser. No. 08/539,721 filed Oct. 15,1995, now abandoned, which is a divisional of 08/188,750, filed Sep. 1,1993, now U.S. Pat. No. 5,507,927, which is a continuation ofapplication Ser. No. 07/828,131 filed Jan. 30, 1992, now abandoned,which was a continuation-in-part of Ser. No. 07,463,491, filed Jan. 11,1990, now abandoned.

FIELD OF THE INVENTION

This application relates to a method and apparatus for the reduction oforganic materials using microwave radiation.

BACKGROUND OF THE INVENTION

There are numerous instances in diverse areas where it is desirable thatorganic materials be reduced. Such a requirement may arise in theprocessing of raw materials, as, for example, in the extraction of oilfrom oil shales, or in the treatment of waste materials.

The waste treatment category will arise in an endless number ofsituations. This may be due to the useful life of the product havingbeen completed. For example, huge quantities of worn out tires are inexistence. The waste may also arise from normal industrial processes.Refinery sludge and pulp mill effluents are examples. Municipal sewageand garbage are other sources of large quantities of organic waste.

Various considerations dependent on the particular waste type mandatethat the waste be treated. In the case of municipal sewage, for example,the waste is a health and environmental hazard and its toxicity must beneutralized. In the case of tires the emphasis is on recycling of thevery substantial amounts particularly of oil and carbon black which arethe major components of tires.

The treatment of various of these waste types as, for example, byburning, may itself lead to environmental pollution problems.

There is therefore an ongoing need for more efficient treatment andrecycling methods for organic materials.

Against this background the present invention is directed toward the useof microwave energy in a method and apparatus which is applicable in avery general sense to a very wide range of organic materials.

PRIOR ART

Applicant is unaware of any prior use of microwave energy in thetreatment of organic materials for non-pyrolytic reduction purposes.Canadian Patent No. 1,158,432, issued Dec. 13, 1983, to Tillitt,suggests the use of microwave energy in drying bulk materials such asgrains. The patent offers no aid to the reduction problem discussedabove.

U.S. Pat. No. 4,123,230, granted Oct. 31, 1978, to Kirkbride, suggeststhe use of multiple wave sources, but these are used to providemicrowaves of different frequencies. There is no suggestion of focusingnor of creating a uniform or preferred distribution pattern.

U.S. Pat. No. 4,184,614, granted Apr. 10, 1979, also to Kirkbride,describes a somewhat different process than that set out in thepreceding reference but contains the same material in respect of themicrowave energy.

Similarly, a third Kirkbride patent, U.S. Pat. No. 4,234,402, issuedNov. 18, 1980, describes the same microwave generator arrangement.

U.S. Pat. No. 4,376,034, granted Mar. 8, 1983, to Wall, shows use of apair of microwave generators at opposite ends of a reactor. A veryinefficient use of reflected waves is the basis of this microwaveapplication.

The prior art has generally not addressed itself to the more efficientuse of microwaves, but has simply incorporated into various processescommercially available microwave generation systems.

BRIEF SUMMARY OF THE INVENTION

It has now been determined that a wide variety of organic materials canbe treated with microwave energy for controlling toxicity, for recyclingpurposes and for various processing purposes.

Thus the invention provides a method for the controlled non-pyrolyticreduction of organic materials which method comprises subjecting thematerials to microwave radiation in a reducing atmosphere.

In a further embodiment of the invention there is provided a method forthe non-pyrolytic breakdown of longer chain molecules in organicmaterials which method comprises subjecting molecules to microwaveradiation in a reducing atmosphere.

In a further embodiment there is provided an apparatus for thecontrolled non-pyrolytic reduction of organic material by microwaveradiation comprising a microwave chamber, means for feeding the organicmaterial into the chamber, at least one microwave generator in thechamber, means for removing gaseous products from the chamber and meansfor removing solid residues from the chamber.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 illustrates schematically the method according to the invention:

FIG. 2 illustrates schematically a microwave generator and parabolicwave guide for use in the invention; and

FIG. 3 illustrates a pattern for application of microwaves in apreferred embodiment of the invention.

While the invention will be described in conjunction with preferredembodiments, it will be understood that it is not intended to limit theinvention to such embodiments. On the contrary, it is intended to coverall alternatives, modifications and equivalents as may be includedwithin the spirit and scope of the invention as defined by the appendedclaims.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

In the following description, similar features in the drawings have beengiven similar reference numerals.

The method and apparatus of the invention can be applied to an almostlimitless variety of organic materials. It is believed that themicrowave energy results in the severing of weaker molecular bonds inlonger chain molecules to reduce those molecules to simpler forms. Thisis in effect a de-polymerization process. The process is controlled toavoid pyrolysis of the organic material.

A general schematic of the invention is illustrated in the drawing.Materials are fed into a hopper 10 or into a similar means suitable tothe particular feed material.

The material is then fed via an air lock 12 into a microwave chamber 14.The material is irradiated by microwave energy from magnetrons 16.

Gaseous products are taken off to a condenser 18 and condensed to liquidproducts, generally oils and sulfur.

Solid residues exit the chamber 14 through a second air lock 20. Theseproducts are than separated, as by screen 22, into various groups.Carbon black will normally comprise a substantial part of theseproducts. Others would include, for example, steel in the case of tirereduction.

Optimum process conditions and apparatus configuration will be selectedfor a given material after an initial analysis of that material. Severaltypes of analyses are preferably carried out with differing objectives.

Thus, an initial analysis of shape and structure may be made with a viewto adapting the microwave chamber and the feeder means to that material.For example, the toroidal shape of tires suggests a different feeder andchamber design than, say, a cube of compressed plastic scrap.

A further analysis is then preferably performed on the material todetermine its composition. For example, in treating material which mightbe categorized essentially as PVC, one would also like to know thequantities of extenders and other such components which might bepresent.

The results of this analysis will provide information as to the productswhich are likely to be obtained from the breakdown of the material, thequantities of each such product that might be expected and the order inwhich the products are likely to be obtained.

A further analysis is then carried out, generally by lab testing, todetermine the energy requirement for the process. Having determined thatrequirement per unit of throughput material, and knowing the volume ofmaterial required to be processed, the total energy requirement can becalculated.

The result of these analyses can then be used to optimize apparatusdesign and process conditions for the various stages in the process.

In the flow of material through the process the first area of concern isin the feeding arrangement.

While the process can be carried out on a batch basis, it is muchpreferred that it be continuous. Accordingly, since the microwavechamber must be sealed, the feeding apparatus must meet thisrequirement. One such feeding apparatus design which is useful with avariety of feed material is a piston and cylinder arrangement. For solidfeeds a feed hopper can be located above and toward one end of acylindrical feed conduit to deliver feed material to the conduit. Apiston may then be utilized to move the material along the conduittoward the microwave chamber. The continuous plug formed in the feedconduit by the feed material will serve to seal the inlet to themicrowave chamber.

A second preferred apparatus for bulk materials and relatively lowtemperature operations is in the form of an endless belt conveyor. Thebelt material must be permeable to microwaves and must not itself breakdown under conditions of use.

For higher temperature operations another preferred feed apparatuscomprises one or more stainless steel screw conveyors.

For certain material configurations an airlock may be introduced at theentry to the microwave chamber.

Similarly, in some cases an airlock will be necessary at the solidsoutlet from the microwave chamber.

The next consideration in the flow of material through the process isthe shape of the microwave chamber itself.

Several factors will influence the physical characteristics of themicrowave chamber into which the feed material is introduced. Theoverall shape of the chamber will generally be chosen based on thephysical characteristics of the feed material and the type of feedapparatus utilized. For example, where the piston and cylinder feedarrangement is utilized, a cylindrical chamber may be chosen, where anendless belt conveyor is utilized, a chamber of rectangularcross-section will generally be preferred.

The overall shape is also influenced by the desire to obtain maximummicrowave penetration into the material being processed.

Having determined total power requirements and a basic cross section forthe chamber, other factors come into play for purposes of optimization.

A number of variables in the process and apparatus can be predeterminedfor a given application or controlled in the course of carrying out themethod. For a given application the objective is to obtain the mostefficient operation in terms of energy applied per unit mass of materialprocessed, always subject to various process constraints to bediscussed.

The manner of applying the total energy requirement in a given case isgenerally established by a balancing of factors. In order to supplysufficient energy to initiate the reaction in a reasonable time and thento obtain the desired products from the material in the desiredsequence, one must appropriately control applied energy. Thus, the basicmicrowave generation may be obtained from multiple small wave generatorsrather than from a single magnetron. The output from the wave generatorsmay be continuous, pulsed or otherwise varied. The strength of themicrowaves generated can be varied by varying the power input to thegenerators.

A typical chamber of rectangular cross section might include 4transverse rows of 3 microwave generators each.

In addition to the arrangement and power of the wave generators, theenergy applied per unit mass of treated material will be effected by thetime of exposure of the material to the microwave; that is, the dwelltime of the material. The energy factors must at this point again betaken in context with chamber geometry. Thus, dwell time may be directlyaffected by the rate of feed of the material being processed, but, aswell, the length of the chamber may be varied and the mass underbombardment may be varied by varying the capacity of the microwavechamber.

Furthermore, the focus of the microwaves contributes markedly toefficiency, and parabolic wave guides have been developed to provide afocus for the waves from a given generator. A series of wave guides maybe used with a series of wave generators to provide an overlappingseries of microwave curtains to allow very good control of the amount ofenergy applied to the material.

The surface temperature of the material strongly effects microwaveabsorption by the material, so it is highly preferable that the surfacetemperature be monitored and that the power input to the microwavegenerators be adjusted as required to obtain optimum surfacetemperature. Thus, as the reactions proceed as the material movesthrough the microwave chamber, less energy input may be required tomaintain optimum surface temperature, so that downstream microwavegenerators may be operated at lower power input.

It is also useful to monitor the internal temperature of the material inthe microwave chamber as a means of predicting what products are likelyto be coming off the material at any time. The microwave chamber ispreferably kept at slightly above atmospheric pressure. The pressurefacilitates removal of gaseous products.

It has been found that the process works better in a more denseatmosphere. Accordingly, after the process is started up and run to thepoint where the first of the material fed into the chamber has beensubstantially broken down, the process is found to proceed moreefficiently. In that regard the process must be carried out in areducing atmosphere, and the concentration of reducing gases isincreased as the material is broken down. It is theorized that thepresence of additional reducing gases may tend to aid in furtherbreakdown of the material, particularly at its surface.

It may be preferable in some instances to utilize a two part chamber toisolate the wave generators from the reducing atmosphere. A horizontalmicrowave permeable gas impermeable barrier would be one solution, withthe top and bottom parts of the chamber both being resonant.

It may be necessary to add a reducing gas with the feed material. Thepurpose of the reducing gas is to damp out any oxidation which mightotherwise occur during start-up with possible catastrophic results. Aninert gas such as nitrogen might also be used, but any compatiblereducing gas will do. It should be noted that it is not generallynecessary that a reducing gas be added, but that the possibility existsin certain instances.

It has been found that some catalysts enhance the efficiency of theprocess. Thus, the addition of carbon black to the input material in thecase of tires results in the oils coming off the material more quicklyand at lower temperatures.

A further external factor will frequently be present which will be ofprimary concern in terms of the balancing of the internal factors. Thephysical space available in a plant to accommodate apparatus accordingto the invention is often limited, so all of the controllable factorsmust be balanced in the face of that restriction. The importance of thisspace consideration is highlighted by the fact that some installationsmay have a substantial overall length. For example, lengths in the orderof 30 to 60 feet will not be unusual.

In that regard a preferred approach is to utilize a series of modulesconnected end to end. This has several advantages. Among these is theability to remove and replace a single module to carry out repairs,thereby avoiding downtime. A further advantage is in ease of manufactureand handling of smaller modules. A preferred module is about 6 feet inlength overall.

Power availability is a further external variable which may be beyondthe control of a user, usually because of the particular location of theplant.

The products of the process are obtained in the form of gaseous andsolid material. The gaseous materials are recovered utilizing one ormore aspirators on the microwave chamber. The solid products are in theform of residues conveyed through a microwave chamber outlet.

The gaseous products are condensed to provide various hydrocarbonliquids. In that regard it may be necessary to provide heat to theexhaust system to prevent premature condensation.

The solid products comprise carbon black in micron size and variousinorganic materials which may have been present in the feed. Forexample, in addition to the various oils and carbon black obtained fromtires, the residues will include steel, silica and the like components.

For example, a typical PVC lab sample yielded 125 gms solid residue from160 gms of the original PVC. The residue was almost entirely carbonblack containing in total less than 3.159 ppm of the following elementsand compounds: As; Ba; B; Cd; Cr; Pb; Se; U; N0₂ +N0₃ ; N0₂ ; Ag; Hg;CN(F); F.

As a further example, typical tires will yield per tone of tires, 3 to 4barrels of oil, 575 to 700 lbs. of carbon black, 85 to 100 lbs. of steeland 70 to 80 lbs. of fibre.

FIGS. 2 and 3 illustrate a preferred apparatus for carrying out oneembodiment of the invention.

Microwave generators utilized in industrial processes have generallybeen very inefficient in that they have utilized in general thetechnique of heating a material simply by bombarding it in a mannerwhich leads to a very non-uniform distribution of microwave energythrough the material. The result in such cases is that some parts of thematerial are undertreated and others overtreated.

In such cases, in order to ensure that all material receives a minimuminput of microwave energy, a great deal of energy waste occurs.

Furthermore, depending on the material being processed, specificpatterns of applied microwaves may be much more efficient than others.With the commonly used general bombarding approach, such varyingpatterns are not available.

Serious problems of energy loss have also existed in using various waveguide types to distribute generated microwaves. For example, some waveguides have had elongated and non-linear paths and have resulted in onlyweak waves reaching the site of a material to be treated.

Further, a view has been firmly held by some manufacturers of microwaveunits that multiple wave generators are an impractical solution to thedistribution problem because of the problem of interference betweenwaves produced by the various generators The apparatus of FIGS. 2 and 3addresses these problems.

FIG. 2 illustrates a microwave generating apparatus 30 according to theinvention comprising a magnetron 32, an antenna 34 and a reflectingsurface or wave guide 36. The apparatus 30 is illustrated mounted inwall 38 of a microwave chamber 40. The outer extremity 42 of reflectingsurface 36 is mounted flush with wall 38. The opening defined by theextremity 42 of reflecting surface 36 is covered by a ceramic plate 44.

The reflecting surface 36 may be designed to achieve a desired patternof wave application but in the preferred case is substantially parabolicto provide a substantially circular area of wave application. The top 37of the reflecting surface 36 is preferably flattened. This allows foreasy mounting of the unit but also allows the antenna 34 to bepositioned at or near the focus of the parabola.

The boundaries of the pattern may be adjusted by appropriate design ofthe wave guide in combination with a particular placement of antenna 34.The focus of the pattern can subsequently preferably be adjusted byadjusting placement of antenna 34. The antenna 34 is preferablyadjustable over about one inch of travel axially of the reflector 36.

Thus, for example, in the most preferred configuration the combinationof the antenna 34 and reflecting surface 36 is adjusted to provide aslightly off focus application of microwaves so that the diameter of thearea of application of microwaves is greater than the diameter of theextremity 42 of reflecting surface 36.

Application of microwaves is fairly uniform over the circular area.

A series of apparatus 30 can then be arranged as illustrated in FIG. 3to provide the desired overlapping pattern 46, the area of which isdefined by lines 45 through the outer ones 47 of the generators 30 ofthe array. In this configuration there is produced in effect a microwavecloud which will provide a reasonably uniform distribution of microwaveenergy to a material 48 in chamber 40.

In a preferred configuration the apparatus 30 is provided with atemperature sensor 50 mounted in the housing 52 of magnetron 32. Sensor50 is in turn connected by conductors 51 to a controller 54 which willswitch off magnetron 32 via conductors 53 when the sensor 50 registers alimiting temperature and will switch magnetron 32 back on after a presettime period.

Thus, where a non-uniform feed material such as motor vehicle tires isbeing processed, at times there will be no material beneath an apparatus30 as, for example, when the open center part of a tire is passingunderneath the apparatus. In that case waves reflected from the bottomwall 56 of chamber 40 will cause the apparatus 30 to heat up to thepoint where the sensor 50 will send a signal to controller 54 causingthe magnetron to shut down. After a predetermined period which in thetire case would relate to the time required for the open area of thetire to pass the apparatus 30, magnetron 32 will be switched back on.

This has the combined effect of preventing the apparatus 30 fromoverheating, and of saving energy.

While the process is widely applicable, and thus highly variable inconstruction, in a typical case, for example, for reduction of motorvehicle tires, a series of 10 modular tunnels may be used in series toprovide a rectangular tunnel of about 60 feet in length and with a crosssection of about 14 inches by 36 inches. In a preferred embodiment, twosuch 60' tunnels would be used in a tire reduction plant. A series of 12overlapping magnetrons may be used in each module as shown in FIG. 3.Each magnetron may have 1.5 kilowatts of power at a wavelength of 2450MHz.

The typical process will be carried out at a slight positive pressure ofabout 1/4 to 1/2 inch of water and at maximum temperatures of about 350°C. The sensor 50 will typically switch off the magnetron at atemperature of about 70° C.

Typically the reflectors 36 have a diameter of about 71/2 inches to 73/4inches at the extremity of the parabola. The top section 17 is typicallyabout 31/8 inches wide and the reflector about 21/2 inches deep.

In the preferred tire plant with twin tunnels, operating under the aboveconditions, a continuous tire feed rate on a conveyor, running at 3 feetper minute will give a dwell time of about 20 minutes and a throughputcapacity of 1,440 tires per 24 hours for each 60 foot tunnel.

It is notable that this plant would produce no emissions at all. Gaseousproducts consist of a narrow band of oils about the consistency of No. 2diesel fuel, along with elemental sulphur which is condensed separately.

The controlled reduction of the invention avoids emissions problemscommon in other waste reduction processes, including prior microwavebased processes.

What I claim as my invention:
 1. An apparatus for the controllednon-pyrolytic reduction of organic material, said apparatus comprising:amicrowave chamber; means for feeding said material into said chamber; anarray of microwave generators associated with said chamber, said arrayof microwave generators being arranged such that said array transmits asa group in an area of said chamber an overall predetermined pattern ofmicrowave radiation onto said material which radiation is evenlydistributed throughout said area of said chamber; means for monitoringthe temperature of said material in said chamber and for controllingsaid array of microwave generators responsive to said monitoredtemperature so as to avoid significant pyrolysis of said material; meansfor removing gaseous products from said chamber; and means for removingsolid products from said chamber.
 2. The apparatus of claim 1 whereinsaid chamber is cylindrical.
 3. The apparatus of claim 1 wherein saidmeans for feeding comprises a piston and cylinder.
 4. The apparatus ofclaim 1 wherein said chamber is a resonant cavity.
 5. The apparatus ofclaim 1 including at least two said generators arranged in said chamberin an upstream and downstream relationship relative to the flow of saidmaterial.
 6. The apparatus of claim 5 wherein said upstream generator isof greater power output than said downstream generator.
 7. The apparatusof claim 1 including at least one parabolic wave guide for focusing themicrowave output of said generator.
 8. The apparatus of claim 1 whereinsaid chamber is rectangular in cross-section.
 9. The apparatus of claim1 wherein said chamber includes 4 transverse rows of 3 microwavegenerators each.
 10. The apparatus of claim 1 wherein each one of saidarray of microwave generators comprises:at least one microwavegenerator; an antenna connected to each said generator for transmittingmicrowave energy from said generator; and a reflecting surface forreflecting microwave energy from each said antenna in a predeterminedpattern onto said material to be treated.
 11. The apparatus of claim 10wherein said microwave chamber is rectangular in cross-section.
 12. Theapparatus of claim 1 wherein said array comprises 3 rows of 4 microwavegenerates in each row.
 13. The apparatus of claim 1 wherein each saidmicrowave generator in said array generates a substantially circulararea of microwave radiation.
 14. The apparatus of claim 13 wherein eachsaid circular area overlaps with each adjacent circular area such thatsaid overall pattern is continuous across said array.
 15. The apparatusof claim 1 including at least two said generators arranged in saidchamber in an upstream and downstream relationship relative to the flowof said material.